1. Field of the Invention
The invention relates generally to connecting rods and, more particularly, to a hybrid connecting rod made of a light alloy material and a second fatigue life strengthening means for use in internal combustion engines.
2. Description of Related Art
Steel is normally used for construction of automobile connecting rods because of its strength, durability, and lower cost. However, steel with its high mass density exerts excessive stresses on the crankshaft of a high speed engine. This in turn requires a heavier crankshaft for carrying the loads and, therefore, the maximum RPM of the engine is limited. Additionally, higher inertia loads, such as those caused by steel connecting rods and heavier crankshafts reduces the acceleration or declaration rates of engine speed. Therefore, light alloy metals such as aluminum and titanium are currently being used in high speed engine connecting rods to circumvent the above-mentioned problems. Titanium has better mechanical properties than aluminum, at the expense of higher density and cost. This higher density and cost have made aluminum connecting rods more popular and attractive. However, they suffer from relatively low strength and fatigue life.
Particulates such as SiC, Alumina, and a variety of chopped fibers in an aluminum matrix are being used, with limited success, to improve the strength and stiffness of aluminum connecting rods. High modules and strength carbon fibers are the most desirable reinforcements that can be used. In this connection, U.S. Pat. No. 4,425,820 discloses a design with such fibers for construction of a connecting rod. The carbon fibers in the connecting rod of this patent are the primary load carrying member and the aluminum is primarily a casing for those fibers. Proper adherence of fibers to aluminum, inherent weakness due to casting, the shrinkage of aluminum after pouring causes wrinkling of the fibers, and the residual stresses caused thereby are practically insurmountable problems with such carbon fiber containing aluminum connecting rods.
A further prior art connecting rod design is shown in U.S. Pat. No. 4,391,161 which discloses how the buckling capability of a connecting rod used in large long stroke engines can be improved without enlargement of the beam section by the inclusion of stainless steel fibers in the beam flanges. Buckling capability of a connecting rod in a high speed engine is of far less concern. Also, the aforementioned problems with carbon fiber design connecting rods still remain, as well as additional problems with the stress concentration introduced in the aluminum by the ends of the long steel fibers.
In addition to the above, the known prior art designs, even though conceptually sound, have further weaknesses and drawbacks as far as ease of manufacturing is concerned. Therefore, there still exists a long felt need in the art for a durable, low cost connecting rod, that is substantially easy to manufacture and which will stand up to sustained use in today's modern, high speed internal combustion engines, such as those used in automobiles.